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Old 10 June 2019, 20:14   #1
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TWO HARD GUYS: YAMAHA 25hp BMHS 2003 vs 20hp 20CM 1991

The two-stroke Yamaha models of the 80s and 90s are reputed to be hard guys. Just what I need for my 4m inflatable honwave, in which I sometimes embark the family. I can not afford to be lost in the sea because of engine failure. It has ever happened to me, going alone, nothing serious. But if happen going with my wife or the kids ... I know it's over for me to navigate. She is very scared.

I have recently been offered an enduro model of 20 hp from the year 1991. The engine has been little used, and has only sailed in fresh water. By its appearance it would be said that it is very well preserved ... a moment ¿20 hp? But if the enduro is only made in 15 or 25 hp ... I think they have been wrong. Commenting with the owner, he replies that he was told by the nautical mechanic who checked the engine. He will ask again.


This is the "enduro" model

Indeed, after asking again, the mechanic continues to affirm that "it is an enduro, a reliable and robust engine like none, almost unbreakable". But in the sheet it says that it is a model 20C (6A9). It's a weird, unusual model. The 8hp Yamaha CMH model is a legendary engine for its reliability. I understand that this 20C is the same design of the "C series", and maybe that is why the mechanic has been confused. It is not an enduro, but it may be a very safe engine.


The label showing a "20CM 6A9" model

I have a Yamaha 25 BMHS from 2002. This is a model of the "B series" from Yamaha, whose specifications are more sporting. The two engines weigh almost the same, about 50 kg. But the BMHS gets those extra 5hp versus the 20hp of the 20CM. It's another engine design, obviously.

It's not the mine but this one is a 25BMH

And here my great doubt, which one to stay with? Are there significant differences in reliability between the two engines? Which is better in that it does not break while being at sea? I already know that these things depend above all on how careful the engine is and how it has been used. But it is also clear that there are more delicate outboards, while others like enduro do not break even with an intensive and neglected use. I guess the 20CM will be a rude boy, more than the 25BMHS, but I really do not know if there are significant differences.

Anyway, this is the dilemma I have. Welcome any opinion or advice. And very grateful.


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Old 11 June 2019, 01:15   #2
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The 20C in that colour way was known as the “Origin 20” in UK and europe and was part of the Yamaha “Origin” range. These were the older designs of the 20/25/40/55/75/85 and 115. Other parts of the world called them Enduros but the Enduro range differed slightly in the range of models offered.

They were the previous generation of Yamahas that were kept in production and were aimed at commercial users and came with minimal features, no autolube except 115, trim and tilt only available on 55hp upwards, no instruments supplied etc. They were sold alongside the newer range of outboards (autolube / trim and tilt etc) which were known as the “Hi-tech” range at that time and aimed at the leisure user.

The origins were produced in that unique Yamaha Dark Blue colour asin photos above for a few years in early 90s before going grey in 1994/5 in line with the rest of the range.

I would take a good Origin 20 over the later 25N any day. Yes you have to premix fuel but the engine is indeed far more rugged. It is single carb that can be removed in under a minute with 10mm spanner and screwdriver. They will run on poorer fuels as not as high compression ration as the Hi-techs. Everything is easy to get to and not crammed in like the later engines so very easy to work on. So potentially if you had a problem at sea they can be fixed easily. I never liked the 20D/25N, they never run as nicely as the older engines.

You can still get the shallow water tilt kit for it (was an optional extra but some came with it fitted). The 20 can also be uprated to 25hp using the cylinder head and parts of the earlier 25hp (but not a later Origin 25 as this was a derated 30)

The only potential weak point on that engine on a poorly maintained example that has not ever been flushed out after use is the casting where the lower liner is pressed into the block. Corrosion can cause the casting to hairline crack in one particular weak spot in the waterway and in some cases can ovalise the bore at the very top and cause a tight spot. That one above should be fine especially as fresh water used and well maintained.
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Old 11 June 2019, 02:46   #3
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Stunned. I was not expecting a response so complete and rich in information about a rare engine that was manufactured ... in the 80's!

I thought there would be no one who knew about this model. Indeed, the mechanic mentioned that it was an "Origin model, with the same specifications as an enduro", but I did not understand what he meant (now yes, thank you very much Phantom!). Now I also understand the insistence that it is an enduro.

This is what the 20CM looks like inside. It seems to have some rust, not too much, it's not like to worry about it. Although by a picture it is difficult to know.


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Old 11 June 2019, 03:31   #4
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great info there i remember them well when tornado fitted them on their boats in hull at the time.
a must buy IMO Nook good luck
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Old 11 June 2019, 07:03   #5
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They were also sold under the Mariner name and used by the RNLI if I remember correctly.

Check the lower unit carefully, I've seen them with some water in there.

They have a strange sound which could be alarming but it is normal for them - when revved, as the revs drop they knock quite loudly. There was a thread about it some years ago where someone was worried about the knocking.

Also, because they have a starter ring on the flywheel, it only needs a motor and a bit of electrics to convert it to electric start.
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Old 11 June 2019, 07:17   #6
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Yes they always knocked from new when revved and let off when not under load. In use it is not apparent as never in that situation.
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Old 11 June 2019, 07:22   #7
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I had a 2 cylinder Yamaha 25hp (model 25D) circa mid 1980s. Great engines. Not as robust as the Enduro model, but a reliable no nonsense engine none the less.

All engines can fail, so service meticulously, sparks, fuel filter, gear oil and impeller, change starter rope every other season, check thermostat (if fitted) and run in fresh water after every outing if possible.
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Old 14 June 2019, 01:21   #8
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Thank you friends for all the info and your advice!

Tonight will be the purchase. Let's see if later I can upload some video or photo of the engine.

I love these noble and "classic" outboards, it's like someone who restores an old mythical car or motorcycle and proudly takes it as his main vehicle ..
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Old 15 June 2019, 16:16   #9
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Firts picture of the Origin 20 at its new home.

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Old 17 June 2019, 04:08   #10
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Tremendous engine, the SIB was flying!

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